[PATCH][RFC] space saving incrementals

jw schultz jw at pegasys.ws
Tue Mar 12 06:32:11 EST 2002

On Mon, Mar 11, 2002 at 12:41:07PM -0600, Dave Dykstra wrote:
> On Fri, Mar 08, 2002 at 03:05:14PM -0800, jw schultz wrote:
> > On Fri, Mar 08, 2002 at 03:45:04PM -0600, Dave Dykstra wrote:
> > > I like link-dest, and the "-" for exclude-from/include-from was already
> > > something I was planning to add one of these days along with the
> > > --files-from option I still plan to write, but --compare-perms confuses
> > > me.  Can you give examples of when you need it?
> > > 
> > > - Dave Dykstra
> > 
> > sequence of commands:
> > 	admin# rsync /project /vault/monday
> > 	admin# chmod 666 /project/somefile
> > 	admin# chown bin /project/someotherfile
> > 	admin# rsync --link-dest=/vault/monday /project /vault/tuesday
> > 
> > Now /vault/monday/somefile has perms of 666 and
> > someotherfile is owned by bin.  I cannot restore the perms
> > from /vault/monday.  That info is lost. /vault/monday no
> > longer is an accurate representative of what existed when it
> > was created.
> > 
> > With --compare-perms somefile and someotherfile will not be
> > linked between monday and tuesday even though the contents
> > haven't changed.
> > 
> > compare-perms only makes sense when you are using link-dest.
> Why not just always do --compare-perms functionality with --link-dest?  I'd
> rather not have more hard-to-explain options if they can be avoided.
> - Dave Dykstra

I personally wouldn't mind.  --compare-perms existed before
--link-dest.  I started by doing a cp -al before the rsync
but that seemed wastefull especially with how little it took
to add the --link-dest onto --compare-dest.

However, i suspect that some others would gripe at rsync
--link-dest not linking if all that changed was file
meta-data.  I could be wrong but i think --link-dest without
a seperate --compare-perms or its inverse might cause more
confusion although users could leave off -pgo if they don't
care about the meta-data.

This may become more of an issue with ACLs and other
extended file attributes.  But that is at least another year
in the future.

By the way, really appreciate rsync.  I tried this with
rdist because it didn't have the permissions problem but the
performnce stank.  Monitoring it i found the slowdown wasn't
bandwith, disk or CPU.  Rsync even did the initial transfer
(nothing on dest) at over 10x the speed with the limitation
being the 350MHz cpu on the backup server.

	J.W. Schultz            Pegasystems Technologies
	email address:		jw at pegasys.ws

		Remember Cernan and Schmitt

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